The present invention relates generally to thermal insulating systems and more specifically to a method for filling insulated glazings.
The use of insulation, weather stripping and other energy conserving products in the construction and renovation of buildings has successfully reduced the energy required for heating and cooling such buildings by impeding the transmission of heat through walls, floors, and roofs. However, even with the construction and use of highly insulated buildings, much energy is unnecessarily wasted in heating and cooling due to heat transmission through windows.
The earliest response to this problem was the development of double glazed windows (R2 - a thermal resistance of 2 hr-ft.sup.2 -deg F/BTU) to replace single glazed (R1) windows. Such thermal window assemblies are usually constructed by placing sealed, insulated glazing ("IG") units having the desired number of glazing layers in conventional window frames. "IG" is used in the art to refer to insulated glass units; however, because the applicants foresee glazing as being comprised of materials other than glass, the term "IG" units when used herein will not refer to a specific material but to insulated glazing units generally. While the addition of further glazing layers to the IG unit provides a moderate gain in insulating performance, it also adds weight and bulk to the window and reduces the transmission of light.
Since radiative transfer is a significant portion of heat transfer in a typical multi-glazed window, low emittance coatings have been developed which reflect long wavelength infrared energy and reduce window heat transfer. The addition of a low-emittance (low-E) coating to a double glazed IG unit provides the thermal efficiency of triple glazing (R3) without the additional weight, bulk and complexity.
Further improvements have been made possible by the addition of a low conductance gas to the space between the low-E glazings to reduce the other major component of heat transfer - conductive/convective heat transfer. For example, U.S. Pat. Nos. 4,459,789 and 3,683,974 disclose the use of various fluorocarbon gases, known collectively by the trademark "Freon," in a sealed window assembly. U.S. Pat. No. 4,393,105 teaches of the use of argon and krypton to serve this purpose.
Conventional methods for filling the space between glazings in IG units, however, are generally wasteful. For example, the method described in U.S. Pat. No. 3,683,974 teaches that gas be introduced through a single opening between the glass panes. As the gas enters the interior space, air is displaced into the outside environment.
Another method involves the use of two openings, one at the top and the other at the bottom of the unit being filled. Gas is slowly injected through the bottom opening to prevent turbulence, pushing air out of the top opening. After the air has been substantially displaced, the filling process is ceased and the holes are plugged.
The above described processes only result in gas/air mixtures of about 80-90% gas. Higher percentage fills are difficult to achieve without structural damage to the glazings or a significant waste of gas and time. Further, these methods are inefficient, causing substantial losses of gas. It is not uncommon for a loss of more than 50% of the gas filling the volume of the space between glazings to occur.
With the current demand for "super windows" that use krypton or other expensive gases, there is a need for a more efficient method of filling IG units. A vacuum chamber can be used during the evacuation and refill process to accomplish this purpose. For example, U.S. Pat. No. 4,393,105 discloses the use of a housing containing a controlled environment where gas fill of the thermal IG units occurs. The method described, however, requires that the housing, as well as the IG units be filled with the gas mixture. Thus, significant amounts of gas must be used. This is undesirable when costly gases are used to fill IG units. Accordingly, there is a need for a more efficient method of filling these units.